The present invention relates to a field-emission display having a faceplate formed with a phosphor layer and means irradiating an electron beam onto the phosphor layer. More specifically, the present invention relates to a display suitable for a field-emission display (hereinafter, called an FED) using a ZnS phosphor.
Various displays are being studied and developed increasingly in image information systems corresponding to various requests of a higher resolution, a larger screen, a thinner type and lower power consumption. Displays using a Braun tube have been used widely. Making them thinner is limited.
In recent years, FEDs have been studied and developed more and more as a display which can realize a thinner type and lower power consumption responding to such requests. In the FED, a plane-shaped field-emission type electron source is disposed on the back surface of an enclosed vacuum box and a phosphor layer is provided in the inner surface of a front faceplate. An electron beam of low accelerating voltage of about 0.1 to 10 kV is irradiated onto the phosphor layer for emission to display an image.
The electron density of the electron beam irradiated onto the phosphor layer is a high electron density as about 10 to 1000 times that of a typical Braun tube. In the phosphor layer for the FED, a low resistance characteristic which causes saturation with electric charge is desired. Further, a good characteristic of life under a high electron density and a high brightness characteristic are required.
To realize the lower resistance, longer life and higher brightness of the phosphor layer, various developments have been made. As a method for improving the performance of the phosphor layer for the FED using a ZnS phosphor, as described in Japanese Laid-Open No. 2000-96046, there is a method in which a mixed phosphor of a sulfide system phosphor and an oxide system phosphor as an yttrium, aluminum oxide system or a silicate system phosphor is provided to offer a good luminescent maintenance factor with time.
As described in Japanese Laid-Open No. 8-127769, there is a method in which a ZnO layer is provided on a sulfide system phosphor layer or ZnO is coated onto the surface of a phosphor particle so as to eliminate sulfur splash, obtaining a high brightness.
As described in Japanese Laid-Open No. 11-241063, there is a method in which a Zn powder metal is added to a ZnS or (ZnCd) S system phosphor to prevent the phosphor from being oxidized, thereby reducing surface charge to improve brightness.
As a method performing for high quality image display by contriving the construction of the FED, as described in Japanese Laid-Open No. 11-185673, there is a method for preventing scattering of an electron beam reflected on a phosphor layer by a black matrix formed to be projected from the emitting surface of the phosphor layer.
As a method related to added concentration of a radiative recombination center device of a ZnS phosphor, as described in Asia Display/IDW' 01 Proceedings, FED 1-2, 1157, there is a method for improving luminescent deterioration by increasing Al and Cu concentration at an [Al]/[Cu] molar ratio around 1.0.
As described in Proceedings of the 289th Phosphor Research Soc. No. 31, pp. 31-38 (2001), there is a method for improving luminescent deterioration using P55 type ZnS: Ag, Al phosphor ([Al]/[Ag] molar ratio=1.06) for a projection CRT having a low initial defect concentration on a phosphor surface.
These are reports in which the [Al]/[Cu] molar ratio (the former) and the [Al]/[Ag] molar ratio (the latter) are around 1.0. A concentration range in which a molar ratio is higher than that is not described.
To realize the lower resistance, longer life and higher brightness of the phosphor layer for FED, various methods have been studied. The prior art methods have not solved all the problems. A new method for lowering the surface resistance of a phosphor to achieve a longer life is required.